Towards odorless cosmetic ingredients: determination of fatty esters odor origin
Podium 44
Presented by: Marie Jaricot
The cosmetic industry is increasingly demanding towards the cosmetic ingredients used in formulations. Fatty esters are no exception; on top of their performance as emollients, emulsifiers, solubilizing or dispersing agents, they are expected to be multifunctional, eco-responsible, ethical, and also to present neutral sensory properties, especially in terms of olfaction. Indeed, an undesirable odor from an ingredient in the formula could significantly impact the final odor of the cosmetic product. The industrial synthesis of fatty esters follows several refining steps to take into consideration these specifications: esterification, neutralization, washing, drying, bleaching, filtration, and finally deodorization. This last step of deodorization is decisive to remove volatile compounds and oxidation products. Nevertheless, some fatty esters may still emit a residual odor even after all these refining steps. Therefore, it is essential to establish the origin of the residual odor to improve industrial refining steps subsequently and propose odorless fatty esters. This subject has been barely studied in the literature: odor thresholds of some fatty esters were evaluated1,2 and volatile compounds generated by thermal degradation of stigmasteryl esters were investigated3 but the studies did not go further. This work aims to bridge the knowledge gap on odorant volatile compounds of fatty esters and understand the mechanism of their formation to optimize deodorization steps.
In this study, a specific analytical methodology was adopted to characterize the residual odor of different fatty esters. First of all, fatty ester samples underwent sensory analyses during which evaluators assessed their odor intensity thanks to an n-butanol in water reference intensity scale and their odor profile with the Langage des Nez® method. Volatile compounds of fatty esters were also extracted from their headspace by Solid-Phase MicroExtraction (SPME) and analyzed by Gas Chromatography coupled to Mass Spectrometry (GC-MS) to be identified and semi-quantified. Furthermore, Gas Chromatography coupled to Mass Spectrometry and Olfactometry (GC-MS-O) analyses were carried out on fatty esters to put forward odor-active compounds amongst previously detected volatiles.
Besides the fatty esters themselves, a substantial number of volatile compounds were put forward by SPME-GC-MS analyses: it could be as high as around 70 released volatiles depending on the fatty ester. These volatile compounds were found in trace amounts in fatty ester samples. Some of them have been established as odor-active compounds thanks to GC-MS-O analyses. It was thus possible to put forward the contribution of specific volatiles to the ester’s overall odor. Some odor-active compounds were also detected into the raw materials of fatty esters (alcohol or acid) and thus came directly from them; while others were seemingly generated during the ester’s synthesis.
Combining chemical and sensory analyses is crucial to understand the odor origin of fatty esters and especially determine odor-active compounds responsible for their residual odor. Indeed, chemical analysis allows identifying volatile compounds released by fatty esters, but not all of them are odorant. Moreover, some odor-active compounds are not detected by chemical analysis because their concentration is below the detection limit of the GC-MS. In some cases, the nose remains a much more effective detector, hence the key role of sensory analysis.
To conclude, this study allowed us to assess the olfactive impact of different fatty esters and to bring to light the odor-active compounds present in trace amounts in the esters. The residual odor origin has been clarified for the greater part. Thus, these results will guide further investigations to improve the fatty ester refining process, especially the deodorization step to develop odorless ingredients. The analytical methodology implemented in this study could also be used further to evaluate the impact of enhanced deodorization methods.
In this study, a specific analytical methodology was adopted to characterize the residual odor of different fatty esters. First of all, fatty ester samples underwent sensory analyses during which evaluators assessed their odor intensity thanks to an n-butanol in water reference intensity scale and their odor profile with the Langage des Nez® method. Volatile compounds of fatty esters were also extracted from their headspace by Solid-Phase MicroExtraction (SPME) and analyzed by Gas Chromatography coupled to Mass Spectrometry (GC-MS) to be identified and semi-quantified. Furthermore, Gas Chromatography coupled to Mass Spectrometry and Olfactometry (GC-MS-O) analyses were carried out on fatty esters to put forward odor-active compounds amongst previously detected volatiles.
Besides the fatty esters themselves, a substantial number of volatile compounds were put forward by SPME-GC-MS analyses: it could be as high as around 70 released volatiles depending on the fatty ester. These volatile compounds were found in trace amounts in fatty ester samples. Some of them have been established as odor-active compounds thanks to GC-MS-O analyses. It was thus possible to put forward the contribution of specific volatiles to the ester’s overall odor. Some odor-active compounds were also detected into the raw materials of fatty esters (alcohol or acid) and thus came directly from them; while others were seemingly generated during the ester’s synthesis.
Combining chemical and sensory analyses is crucial to understand the odor origin of fatty esters and especially determine odor-active compounds responsible for their residual odor. Indeed, chemical analysis allows identifying volatile compounds released by fatty esters, but not all of them are odorant. Moreover, some odor-active compounds are not detected by chemical analysis because their concentration is below the detection limit of the GC-MS. In some cases, the nose remains a much more effective detector, hence the key role of sensory analysis.
To conclude, this study allowed us to assess the olfactive impact of different fatty esters and to bring to light the odor-active compounds present in trace amounts in the esters. The residual odor origin has been clarified for the greater part. Thus, these results will guide further investigations to improve the fatty ester refining process, especially the deodorization step to develop odorless ingredients. The analytical methodology implemented in this study could also be used further to evaluate the impact of enhanced deodorization methods.
(1) Li, C.; Sun, J.; Fu, C.; Yu, B.; Liu, S. Q.; Li, T.; Huang, D. Synthesis and Evaluation of Odour-Active Methionyl Esters of Fatty Acids via Esterification and Transesterification of Butter Oil. Food Chem. 2014, 145, 796–801.
(2) Takeoka, G. R.; Buttery, R. G.; Turnbaugh, J. G.; Benson, M. Odor Thresholds of Various Branched Esters. LWT - Food Sci. Technol. 1995, 28 (1), 153–156.
(3) Raczyk, M.; Kmiecik, D.; Schieberle, P.; Przybylski, R.; Jeleń, H.; Rudzińska, M. Model Studies on the Formation of Volatile Compounds Generated by a Thermal Treatment of Steryl Esters with Different Fatty Acid Moieties. Food Res. Int. 2017, 97, 87–94.